Materials for filling cavities in the body

ABSTRACT

Materials for filling cavities in the body are disclosed which have very high viscosity when in the cavity and a lower viscosity when being delivered to the cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119(e) ofU.S. Provisional Application 60/418,251, filed Oct. 15, 2002,

BACKGROUND OF THE INVENTION

[0002] When using fillers in cavities in the body, especially brainaneurysms, it is highly desirable that the filling material has a highviscosity to ensure that the material, after delivery, will not flow outof the cavity. It can be stated as a general rule, the higher theviscosity of the fluid in the aneurysm, the better.

[0003] This desirability of this high viscosity is offset by the problemof delivering these materials. They are necessarily transferred todistant locations through long tubes with very small diameter. Thesetubes need to be passed through torturous vessels to access theaneurysm. The transport of high viscosity materials through these tubesresults in high shear stresses. This results in very high deliverypressures and requires very robust catheters. Robust catheters, bynecessity, have thick wall and accordingly are not very flexible. Thesetypes of catheters are hard if not impossible to be passed through thetortuous vasculature upstream of the aneurysm. As a general rule, thelower the viscosity of the fluid being delivered, the better.

[0004] In the systems used today, there is a trade-off between theviscosity of the material in the aneurysm (the higher the better) andthe viscosity of the delivery material (the lower the better). Generallythis trade-off is resolved by using a material that has some compromiseviscosity. Even at this compromise viscosity, one has material thatbehaves marginally in the aneurysm which also requires expensive andstiff delivery catheters.

DETAILED DESCRIPTION OF THE INVENTION

[0005] Pseudo-Plastic Materials

[0006] General

[0007] Pseudo-plastic materials are ones whose viscosities decrease withshear. The apparent viscosity of these materials decreases when they arepushed through tubes. The apparent viscosity increases once the flow hasstopped. Some of these changes are time dependent (thixotropic) and someare almost instantaneous. Both types of materials can be used.

[0008] The characteristics of these types of fluid are shown if FIG. 1.These fluids have a low viscosity when being delivered (some shear rate)and a higher viscosity after they have exited the catheter (no shearrate).

[0009] The advantage of using pseudo-plastic solutions is obvious fromthe above figure. Generally, the allowable viscosity of the fluid isdetermined by what can be delivered in a practical system (catheter witha given length and diameter) at a practical flow rate. This will definea certain shear rate (Point B).

[0010] The viscosity of the fluid in the aneurysms is the viscosity ofthat material at zero-shear rate. When using a pseudo-plastic material,the viscosity at rest, Point A, is much greater than the viscosity of aNewtonian material, point C. Use of a pseudo-plastic instead of aNewtonian fluid will allow one with a given delivery system to deliver amaterial with a higher at-rest viscosity. The higher the degree of shearthinning the better.

[0011] Bingham Plastics

[0012] Bingham plastics are materials that do not flow at all until youthey experience a certain critical stress. Once this critical stress hasbeen reached, they flow freely. They can be considered to be a specialcase of pseudo-plastic materials.

[0013] Toothpaste is an example of a Bingham plastic. When it is notsqueezed (stressed) it stays put and acts like it has an infiniteviscosity. Once you get it flowing, if flows quite freely. Once it getswhere you want it to go, the toothbrush, it then acts like it has aninfinite viscosity again. A Bingham plastic could be an ideal materialfor filling aneurysms.

[0014] Sources of Materials

[0015] Methods for obtaining solutions that exhibit pseudo-plasticbehavior include:

[0016] 1. Formulating a compound which exhibits the behavior and usingit directly

[0017] 2. Adding substances to an existing non/less pseudo-plasticsolution (so call thickening agent).

[0018] Examples of these pseudo-plastic enhancing agents include:

[0019] 1. Adding small fillers to the material

[0020] i. Calcium carbonate

[0021] ii. Barium Sulfate

[0022] iii. Ground up filler agent itself

[0023] iv. Carbon beads

[0024] v. Silica

[0025] 1. fumed

[0026] 2. small particles

[0027] vi. TiO2

[0028] vii. Magnetic materials

[0029] viii. Etc.

[0030] 2. Adding a quantity of dispersed fiber

[0031] 3. Adding highly pseudo-plastic polymer solutions.

[0032] 4. Combinations of the above.

[0033] Transitional Systems (Switched Systems)

[0034] There are other ways to cause a low viscosity liquid totransition to a high-viscosity material when delivered. These includematerials that:

[0035] 1. change an intrinsic property (gets more viscous due to areduction of temperature)

[0036] 2. change state (for example: from a liquid to solid),

[0037] 3. undergoes a phase transition (visco-elastic material to aglass)

[0038] 4. change in structure (the materials increased its molecularweight or cross links).

[0039] Several means of initiating these transitions are outlined below.

[0040] 1 Delivering the material at one temperature (generally warm) andcooling it in the cavity.

[0041] 2 Initiate a chemical reaction—i.e. put an initiator in apre-polymer, and then imitating a chemical reaction as it enters theaneurysm.

[0042] a This can be done continuously as it enters

[0043] b or alternately delivering it and then initiating the reaction.

[0044] Reactable Materials

[0045] Generally, the reactable materials would be pre-polymers ormonomers with an initiator in them that is activated when the materialenters the aneurysm. There are numerous ways of initiating a reaction ofthe mass exiting the catheter including:

[0046] 1 Heat

[0047] 2 Light (see FIG. 2)

[0048] 3 Addition of a second compound

[0049] 4 Loss of a material by diffusion

[0050] 5 Magnetic energy

[0051] 6 Time (use a material that sets up with a known initiation time)

[0052] 7 Etc.

[0053] Ideally the reactable material is a substance that if it doesescape the cavity and goes into the blood stream, it is relativenon-toxic and it dissolves or rapidly breaks down as not to form emboli.Example of these includes blood soluble pre-polymers that cross linkwhen reacted into a non-soluble form. Another way of doing this is touse soluble material to fill the aneurysm and then capping it with anon-soluble material.

SUMMARY OF THE INVENTION

[0054] The ideal solution to the problem is to use a material that has avery high viscosity when it is in the aneurysm and that has a lowviscosity when it is being delivered.

[0055] There are several ways one could develop a material that has alow viscosity when being delivery and a high viscosity at the deliverypoint. These include:

[0056] 1. using a highly pseudo-plastic material or a Bingham plastic asthe filler.

[0057] 2. using a low-viscosity material and then rapidly switching thisto a high-viscosity material in the aneurysm.

[0058] Additional advantages and novel features of the invention will beset forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059]FIG. 1. The viscosity of the pseudo-plastic solution gets less atthe shear rate (flow through a tube) increases. The viscosity of aNewtonian fluid stays constant. A pseudo-plastic solution has a higherviscosity at rest than it does when it flows.

[0060]FIG. 2. A schematic view of a composition of the invention beingused with light activation to provide a high viscosity reacted mass.

I claim:
 1. A material for filling a cavity in the body which has a veryhigh viscosity when in the cavity and a lower viscosity when beingdelivered.
 2. The material of claim 1 comprising a highly pseudo-plasticfiller.
 3. The material of claim 1 comprising a Bingham plastic filler.4. A method of filling a cavity in a body comprising delivering amaterial of claim 1, 2 or 3 to the cavity at a lower viscosity andretaining the material in the cavity at a high viscosity.